Technical Abstract:
This series of studies was designed to evaluate whether pigs which are genetically resistant to Toxoplasma gondii infection could be identified and to determine the genes involved in this resistance. Surveys indicate that T. gondii infection is common in pigs. Among food animals pigs are considered the most important source of foodborne infections in the U.S. Despite the extensive literature on resistance and immunity to T. gondii in mice and humans, almost nothing is known of swine control of this infection. Results: Minipigs of different swine leukocyte antigen (SLA) haplotypes were challenged with ~500 T. gondii oocysts and their response evaluated for a period of 6 weeks after infection. SLAdd pigs were more resistant to this protozoan parasite infection and exhibited a heightened production of interferon-gamma (IFN-g) in the first 2 weeks following infection. Serologic titers were variable and were not correlated with decreased parasite burden. Increased numbers of CD4+/CD8+ cells were found at days 6-10 of infection. Genes other than SLA are involved in controlling complete resistance to this infection; of the 52 pigs evaluated to date only 4 fully resistant pigs have been identified. These studies should provide valuable information on providing genetic methods to control toxoplasmosis in pigs, particularly since vaccination studies have not yielded protocols for which 100% prevention of foodborne parasite transmission can be guaranteed. Thus, identifying genes which endow complete genetic resistance would be a valuable product for pig producers.